1. Field of the Invention
The present invention relates generally to a method of packaging resiliently compressible articles and, more particularly, to a method wherein compressible articles can be conveniently packaged for shipment in a compressed state and can be unpackaged at their destination in a controlled manner.
2. Description of the Prior Art
Many articles of manufacture are lightweight and bulky and cannot be delivered to the consumer without an undesirably high cost associated with shipment. Often these articles are also inexpensive to manufacture but their cost to the consumer necessarily reflects a disproportionately high component of shipping charges, thereby adversely affecting the perceived value of the article to the consumer. One such article whose cost of shipment is undesirably high as compared to its manufactured cost is an innerspring component of a typical mattress, cushion or the like.
In standard mattress construction, for example, an innerspring assembly is used comprising an arrangement of closely packed coil springs. One form of innerspring construction which has proved to be highly successful is known as the Marshall construction. In this construction, individual coil springs are encapsulated in discrete pockets of fabric material with the pockets of fabric material formed together to create strings of coils. These strings of coils are then arranged in an array with the coil springs all oriented parallel to one another, thereby forming an innerspring assembly. An example of such construction is disclosed in U.S. Pat. No. 4,234,983, issued to Stumpf and assigned to the common assignee herein, the disclosure of which is expressly incorporated hereby by reference.
In order to construct a mattress assembly which provides adequate support yet is comfortable to the user, the springs used in the foregoing construction characteristically have such few coil turns and have such relatively weak compressive strength that they can be readily compressed to a size on the order of one-tenth their naturally expanded size. Accordingly, strings of coils of the foregoing type are lightweight and considerably bulky.
Recently, a new construction of mattress has been developed which is capable of being disassembled to knocked down form for convenient shipment to customers or retail outlets. Such a knock down mattress is disclosed in co-pending U.S. patent application Ser. No. 08/398,227 filed Mar. 3, 1995, assigned to the common assignee herein. This construction comprises four bolsters each having a generally rectangular cross section and dimensioned to be arranged in a mattress outline. The bolsters are retained within a shell having a bottom panel, perimeter side panels and a zippered cover panel. Each bolster comprises a fabric casing which contains lengths of pocketed spring coils.
The aforesaid mattress assembly, because of its knock down construction, can be shipped in a highly economical manner by comparison to conventional unitary mattress structures. The components of this mattress can be assembled into packages of very manageable size for shipment. However, it is desirable to provide a packaging method which further reduces the size of the packaging. To this end, vacuum packaging of the coil springs may be employed wherein the strings of coils are compressed within an initially evacuated plastic tube and retained in a compressed state by a containment sleeve fitted over the tube as the vacuum source is removed.
Because conventional springs of the pocketed coil type can be compressed significantly from their naturally extended state, substantial reductions in size of packaging for such springs can be achieved by vacuum packaging methods. However, a disadvantage of using known vacuum packaging methods to provide a compressed package of springs is that once the vacuum source is removed from the inner tube, the springs are entirely dependent upon the presence of the outer containment sleeve for retaining their compressed condition. Thus, once the containment sleeve is severed, such as in opening of the package, the springs can expand to their fully extended state in an uncontrolled and somewhat abrupt manner. The result is that opening of the spring package by severing the containment sleeve with a sharp instrument, for example, can be a surprising and possibly dangerous experience. Accordingly, it is desirable to provide a vacuum packaging method for packaging springs in a manner which permits controlled expansion of the springs upon opening of the package.